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Lipids

Lipids. Lipids are mainly insoluble in water, soluble in organic solvents Uses in cell:. Storage (fatty acids, oils, triacylglycerols, waxes) Membrane/Structural (Phospholipids, glycolipids, sterols)

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Lipids

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  1. Lipids Lipids are mainly insoluble in water, soluble in organic solvents Uses in cell: Storage (fatty acids, oils, triacylglycerols, waxes) Membrane/Structural (Phospholipids, glycolipids, sterols) Signaling, Cofactor, Pigment (phosphatidyinositols, eicosanoids, steroid hormones, vitamins, quinones, dolichols)

  2. Lipids Storage Fatty Acids Hydrocarbon derivatives (highly reduced) Oxidation of fatty acids (CO2 and H2O)is highly exergonic Carboxylic acids with hydrocarbon chains (C4 to C36) Chain can be fully saturated (no double bonds) and unbranched Chain can be unsaturated (double bonds) and branched Naming #carbons : #double bonds Most common FA have an even number of carbon atoms Most double bonds at C9, C12, C15

  3. Lipids Storage Fatty AcidsMelting points Lower for unsat’d because it takes less thermal energy to disorder unsat’d sat’d

  4. Lipids Storage Triacylglycerols (triglycerides, fats) Fatty acid esters of glycerol Three fatty acids each in ester linkage to 1 glycerol Insoluble in water

  5. Lipids Storage Triacylglycerols (triglycerides, fats) In vertebrates, adipocytes (fat cells) store lots of triacylglycerols as fat droplets In seeds, stored as oils for energy Lipases catalyze hydrolysis of triacylglycerols (when need fuel) How is stored fat better than stored polysaccharides (carbs)? (1) Fatty acids more reduced and oxidation produces 2x energy gram for gram (2) Fatty acids hydrophobic so no associated water to carry around Fat stores could meet energy needs for long time BUT human body can only store less than one day’s energy as polysaccharide

  6. Lipids Storage Triacylglycerols (triglycerides, fats) Some animals use fat stores as insulation (seals, walruses, penguins) Hibernating bears use fat stores as energy and insulation Sperm whales use fat stores to match buoyancy of their bodies to surroundings deep under water 4 tons oil (triacylglycerols & waxes) Liquid at 37 ˚C, frozen at ~30 ˚C During deep dives for food oils crystallize and become denser Deep under water, water gets colder and denser Buoyancy of whale changes to match buoyancy of seawater

  7. Lipids Storage Waxes (storage and water repellent) Esters of long-chain (C14 to C36) sat’d and unsat’d fatty acids with long-chain alcohols (C16 to C30) Plankton - storage of fuel Skin glands - secrete wax to protect hair, skin Birds - secrete wax on feathers to keep them water-repellent Plants - wax to protect against parasites and to prevent evaporation Bees - beehive made of beeswax is water-repellent Lanolin - from lamb’s wool used as ointment

  8. Lipids Structural in Membranes Membrane lipids are amphipathic (amphiphilic) - one end is hydrophobic and the other is hydrophilic Directs packing into micelles, bilayers (membranes), liposomes Membrane lipids: Phospholipids - (glycerophospholipids & sphingolipids) hydrophobic region attached to polar group by phosphate Glycolipids - (sphingolipids & galactolipids) hydrophobic region attached to polar group (sugar) Sterols - rigid system of four fused hydrocarbon rings

  9. Lipids Structural in Membranes I. Glycerophospholipids (phosphoglycerides) Two fatty acids attached in ester linkage to C1 and C2 of glycerol Highly polar or charged group attached through phosphodiester to C3

  10. Lipids Structural in Membranes Interesting Phospholipids with ether linkages Found in animal tissues and some unicellular organisms Vertebrate heart tissue Leukocytes Stimulates platelet aggregation Stimulates serotonin release (vasoconstrictor) Role in inflammation, allergic response

  11. Lipids Structural in Membranes II. Sphingolipids 1 sphingosine, 1 long-chain FA, 1 polar head group Structural parent of sphingolipids Phospholipid Glycolipids Neu5Ac - N-acetylneuraminic acid (sialic acid) Negative charge GalNAc - N-acetyl-D-galactosamine

  12. Lipids Structural in Membranes Sphingomyelin Plasma membrane of animals Prominent in myelin (sheath that surrounds and insulates axons of neurons)

  13. Lipids Structural in Membranes Glyco/Sphingolipids Carbohydrate part of certain sphingolipids define human blood group Type O (46%) - universal donor, accept blood from O Type A (42%) - give blood to A or AB, accept blood from A or O Type B (9%) - give blood to B or AB, accept blood from B or O Type AB (3%) - give blood to AB , universal acceptor

  14. Lipids Structural in Membranes Phospholipid and Sphingolipid degradation Cells degrade and replace membrane lipids Problems in development Paralysis Blindness Death by 3/4 years old Infant Mental retardation, death

  15. Lipids Structural in Membranes III. Sterols Present in most eukaryotic cell membranes, bacteria cannot synthesize sterols Cholesterol amphipathic Sterols are also precursors to Steroid hormones potent biological signals that regulate gene expression

  16. Lipids Signals, Cofactors, Pigments Potent signalers - Hormones Enzyme cofactors - involved in electron-transfer in chloroplasts and mitochondria Pigment molecules - conjugated double bonds, absorb visible light, light-capturing in vision and photosynthesis Produce natural coloration of pumpkin, carrots, canary feathers

  17. Lipids Signals, Cofactors, Pigments Phosphatidyinositols Intracellular signals

  18. Lipids Signals, Cofactors, Pigments Eicosanoids Paracrine hormones - Carry messages to nearby cells Involved in reproduction, inflam, fever, pain, blood clotting, etc. Derived from arachidonic acid, 20:4 (5, 8, 11, 14) Three types: prostaglandins, thromboxanes, leukotrienes Anti-asthmatic (prednisone) Prostaglandins (PG) First found in prostate gland, stimulate contraction of smooth muscle of uterus during labor and menstruation, affect blood flow, cause fever, inflammation and pain Thromboxanes (TBX) Produced in thrombocytes (platelets), act in blood clotting Leukotrienes (LT) Found in leukocytes, induce contraction of muscle lining lung airways, overproduce LTs - asthmatic attacks NSAIDS (non-steroidal antiinflammatory drugs) - aspirin, ibuprofen, acetominophen - inhibit synthesis of PGs and TBXs Anti-asthmatics - prednisone

  19. Lipids Signals, Cofactors, Pigments Steroid Hormones Oxidized derivatives of sterol After synthesis move through blood on protein carriers to target Enter cell, bind to receptor, trigger effect Hormones have high affinity for receptors, so very low concentration needed to produce effect

  20. Lipids Signals, Cofactors, Pigments Vitamins (Hormone precursors) Needed for health, cannot be synthesized in body, need to get in diet Fat-soluble (A, D, E, K) Vitamin D Found in milk, butter Vitamin D deficiency - defective bone formation, rickets (need sunlight) Vitamin D3 - formed in skin from 7-dehydrocholesterol & UV light regulates metabolism of calcium uptake in kidney, intestine, bone Vitamin A (retinol) Hormone and visual pigment of vertebrate eye Found in fish oils, liver, eggs, whole milk, butter -carotene (pigment in carrots) can be converted to vitamin A Deficiency - dry skin & eyes, retarded development, night blindness Retin-A Severe acne Wrinkled skin Helps rod and cone cells in retina respond to light

  21. Lipids Signals, Cofactors, Pigments Vitamins E and K and Lipid quinones Vitamin E Associate with cell membranes Destroy oxygen radicals Found in eggs, oils, wheat germ Deficiency - scaly skin, muscle weakness Vitamin K Undergoes redox during formation of prothrombin Vitamin K deficiency slows blood clotting Newborns given a 1 mg injection of vitamin K K1 found in green plant leaves Warfarin (cumadin) Rat poison - causes internal bleeding Anticoagulant drug to treat those at risk of blood clotting Ubiquinone electron carriers in the redox reactions that drive ATP synthesis in mitochondria and chloroplasts

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